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ASD TECHNICAL REPORT 61-326 h CPBEST AV,,-
BEST AVAILABLE COPY
DETERMINATION OF THE MINIMUM SIZED PARACHUTE* REQUIRED FOR STABILIZATION Of THEj A-22 CARGO CONTAINER
HIELMIUT G. HEINRICHI
C. SJIUJKIY K. IBRAHJIM
DEPARTMENT OF AERONAUTICAL ENGINEERINGUNIVERSITY OF MINNESOTA
NOVEMBER 1961
This report is not to be announcedor distributed automatically
in accordance vithAFII 205-43A, paragraph 6d.
AERONAUTICAL SYSTEMS DIVISION
NV, C)C
ASD TECHNICAL REPORT 61-326
DETERMINATION OF THE MINIMUM SIZED PARACHUTEREQUIRED FOR STABILIZATION OF THE
A-22 CARGO CONTAINER
HJELMUT G. HEINRICHAND
SIIUKRY K. IBRAHIM
DEPART; JNT OF AERONAUTICAL ENGINEERINGUNIVERSITY OF MINNESOTA
NOVEMBER 1961
AERODYNAMIC DECELERATOR BRANCHFLIGHT ACCESSORIES LABORATORY
CONTRACT No. AF 33(616)-6372PROJECT 6065
TASK 60252
AERONAUTICAL SYSTEMS DIVISIONAIR FORCE SYSTEMS COMMAND
UNITED STATES AIR FORCEWRIGHT-PAT'ERSON AIR FORCE BASE, OHIO
200 -January 1962 - 19-777
FOREWORD
This report was prepared by the Department of Aeronautical
Engineering of the University of Minnesota in compliance with
US Air Force Contract No AF 33(616)=637.
The work being accomplished under this contract is
sponsored jointly by QM Research and Engineering Command, Depart-
ment of the Army; Bureau of Naval Weapons, Department of the
Navy; and Air Research and Development Command (now designated
Air Force Systems Command), Department of the Air Force, and
is directed by a Tri-Service Steering Committee concerned with
Aerodynamic Retardation. Contract administration is conducted
by Aeronautical Systems Division and Mr. Rudi J. Berndt of the
Aerodynamic Decelerator Branch, Flight Accessories Laboratory,
Wright Air Development Division, is Project Engineer.
Messrs. Edward Holmbeck and Bruce Gniffke and a number
of graduate and undergraduate students contributed significantly
to this study, and the authors wish to express their apprecia-
tion to them.
ASD TE 61-326 i
ABSTRACT
An investigation to determine experimentally the minimum
size and cptimum type of parachute for stabilizing general aerial
delivery cargo and more specifically, the A-22 Cargo Container,
was conducted. It was found that a 4 ft ribless guide surface
parachute in connection with a riser at least 10 ft long repre-
sented the desired optimum. A 64 in. ribbon parachute with
20% geometric porosity in connection with a minimum riser length
of 10 ft appeared also to be quite satisfactory.
In addition, the investigation provided sufficient data
for the calculation of trajectories for different configurations
and release conditions.
PUBLICATION REVIEW
This report has been reviewed and is approved.
FOR THE COMMANER:
George A" Solt, Jr. .Chief, Retardation and Recovery BranchFlight Accessories Laboratory
ASD TR 61-326 iii
This document contains
blank pages that were
not filmed
TABLE OF CONTENTS
Section Page
I. INTRODUCTION ........... ................... 1
1.1 A-22 Container and Standard Aerial Delivery
System ..... .......... ........ ...... 1
1.2 High Velocity Aerial Delivery ..... .......... 2
II. EXPERIMENTAL EQUIPMENT ......... .............. 2
2.1 Wind Tunnel .......... .................. 2
2.2 Model Mounting Frame ...... .............. 4
2.3 A-22 Container Models . .................. 8
2.4 Parachute Models ........ ................ 8
2.5 Strain Gage Moment Balance ... ......... ... 13
2.6 Strain Gage Drag Balance .... ........... .. 13
2.7 Attitude Measuring Devices ... ........... .. 16
2.7.1 Container Angle Measuring Device . . .. 16
2.7.2 Parachute Angles Measuring Device . . .. 16
2.8 Parachute Risers ....... ............... .19
III. EXPERIMENTAL PROCEDURE AND RESULTS .. ......... ... 24
3.1 System of Reference ..... ............. ... 24
3.2 Test Reynolds Numbers .... ............. ... 26
3.3 Critical Container Configurations ........ ... 26
3.3.1 Critical Container Orientation ..... ... 26
3.3.2 Critical Container Height ........... .27
3.4 Tests with Container Model Alone ........ . 27
3.4.1 Moment Characteristics .. ......... ... 27
3.5 Tests with Parachute Stabilized Container
Model Without Risers .... ............. ... 30
3.5.1 Moment Characteristics .. ......... ... 30
iv
Section Page
3.5.1.1 Tests with Parachute Models
Representing Solid Flat, Ribbon,
and Ring Slot Parachutes of
128" Dia. and a Ribless Guide
Surface Parachute of 96" Dia . 32
3.5.1.2 Tests with Parachute Models
Representing Ribbon and Ring
SloL Parachutes of 96" Dia
and a Ribless Guide Surface
Parachute of 72" DIa ... ...... 34
3.5.1.3 Tests with Parachute Models
Representing Solid Flat,
Ribbon, and Ring Slot Para-
chutes of 64" Dia. and aRibless Guide Surface
Parachute of 48" Dia .. .... .37
3.5.2 Drag Characteristics ... .......... 40
3.5.3 Parachute and Container Free Attitude
Angles ...... ................. . 43
3.6 Tests with Parachute Stabilized Container
Models with Risers ...... .............. 47
3.6.1 Moment Characteristics ..... ....... 47
3.6.1.1 Tests Representing 96" Ribbon
and Ring Slot Parachutes and a
72" Ribless Guide Surface
Parachute ... ........... .47
3.6.1.2 Tests Representing 64" Ribbon
and Ring Slot Parachutes and
48" Ribless Guide Surface
Parachute .... .......... 51
3.6.2 Drag Characteristics .... ........ 55
3.6.2.1 Tests Representing 96" Ribbon
and Ring Slot Parachutes and
a 72" Ribless Guide Surface
Parachute ................. 55
v
LIST OF ILLUSTRATIONS
Figure No Page
1. University of Minnesota Horizontal Return WindTunnel - Schematic Layout ...... .............. 3
2. View from Open Test Section Looking TowardsHoneycomb Installed Upstream of Nozzle Assembly . . . 5
3. Pictorial View of Frame and Model Mounting inOpen Test Section .......... ............. . 6
4. General Layout of Model in Wind Tunnel .... ........ 7
5. Details of 1/6 Scale A-22 Container Model Frame . • 9
6. Parachute Model Specifications ..... .......... 10
7. Full Scale Parachute Diameters Corresponding tothe Parachute Models and Different Scale Containers . 11
8. The Ribless Guide Surface Parachute Model andthe Three Scale Models of the A-22 Container . . . . 12
9. General Arrangement and Detail of Moment andDrag Balances ......... ................... 14
10. Moment Balance Calibration ... ............ .. 15
11. Drag Balance Calibration ..... ............. . 17
12. Container Attitude Angle Calibration Curve .. ..... 1.8
13. Parachute Attti.de Meacur1ng Device ........ . 20
14. Parachute Attitude Measuring Device;Design Details and Dimensions .. ........... . 21
15. Parachute Attitude Calibration Curve - Angleip . . 22
16. Parachute Attitude Calibration Curve - Anglee . . 23
17. System of Reference ..... ........... ... 25
18. Moment Coefficient for A-22 Container Model Alonein Original and Re-Oriented Positions .. ........ .28
19. Moment Coefficient of A-22 Container Model Represent-ing 60" and 40" Full Scale Container Heights . . . . 29
vii
Figure No
20. Moment Coefficient for 3 Scale Models ofA-22 Container ....... ................... ... 31
21. Moment Coefficient for Model Systems Representingthe A-22 Container with four Parachute Types withno Risers ......... .................... .33
22. Moment Coefficient for A-22 Container and VariousParachute Models with no Risers ... ........ .. 35
23. Moment Coefficient for Model Systems Representingthe A-22 Container with three Parachute Typeswith no Risers ........ ................... .36
24. Moment Coefficient for A-22 Container and VariousParachute Models with no Risers ............... .38
25. Moment Coefficient for Model Systems Representingthe A-22 Container with four Parachute Types withno Risers .... .... ..................... . 39
26. Moment Coefficient for A-22 Container and VariousParachute Models with no Risers ... ........... .. 41
27. Average Drag Coefficients Based on Container BaseArea for Various Scale Container-ParachuteCombinations with no Risers .... ............. ... 42
28. Drag Coefficients for Various Container-ParachuteCombinations ........... .................... 42
29. Experimental Arrangement of the 1/4 Scale A-22Container in Combination with Three ParachuteTypes with no Risers ....... .............. .45
30. Comparative Stability Behavior of the A-22 Containerwith Various Types of Parachutes and no Risers.Container and Parachute Attitude Angles a and 8Vcrsus Time ........ ................ .. 46
31. Moment Coefficient for Models Representing VariousRiser Lengths and Parachute-Container Combinations . 49
32. Moment Coefficient for Various Parachute-ContainerCombinations and Riser Lengths ... ........... ... 50
33. Moment Coefficient for Models Representing VariousRiser Lengths and Parachute-ContainerCombinations ...... ... ................. .. 52
viii
Figure No Page
34. Moment Coefficient for Various Parachute-ContainerCombinations and Riser Lengths ..... ........... 54
35. Drag Coefficient Versus Riser Length for VariousParachute-Container Combinations .... .......... .56
36. System Drag Coefficient Versus Riser Length forDifferent Parachute Container Combinations .... .. 58
37. Drag Coefficient Versus Riser Length for VariousParachute-Container Combinations ... .......... . 60
38. System Drag Coefficient Versus Riser Length forDifferent Parachute-Container Combinations ..... ... 62
39. Average Drag Coefficients for A-22 Containerand Various Parachute Sizes and Types withVarious Riser Lengths ........ ............... 64
40. Drag Coefficients for Various Container-ParachuteCombinations with Various Riser Lengths ........ . 65
41. Experimental Arrangement of the 1/4 Scale A-22Container in Combination with Three ParachuteTypes with 10 ft Risers .............. 67
42. Comparative Stability Behavior of the A-22 Containerwith Various Types of Parachutes and 10 ft Risers.Container and Parachute Attitude Angles a and 8Versus Time ......... ................... .. 68
43. Mean Attitude Angles a Versus 8 for Models ofA-22 Container and Various Parachutes withDifferent Riser Lengths ..... ............... .. 69
ix
LIST OF SYMBOLS
CD Drag coefficient, general
CDC Container drag coefficient (referred to container base
area)
CD Parachute drag coefficient (referred to container basep
area)
CDo Drag coefficient of parachute canopy based on totalcloth area, So
CDs System drag coefficient (referred to container base
area)
CM Moment coefficient (referred to container base area
and length of base diagonal)
D Drag, general (lb)
Do Nominal canopy diameter
Dp Projected or inflated canopy diameter
H Container height dimension
L Lift, general (ib)
q Dynamic pressure assuming incompressible fluid
(lb per sq ft)
Re Reynolds number
S 0 Total cloth area of a canopy
S Projected area of inflated canopyP
W Weight, general
a Container angle of attack (degrees)
8 Angle of yaw of parachute with respect to the container's
longitudinal axis (degrees)
Angle of pitch of parachute with respect to the con-
tainer's longitudinal axis (degrees).
x
I. INTRODUCTION
The basic objective of this project is to determine the
minimum size and optimum parachute type capable of stabilizing
general aerial delivery cargo and more specifically the United
States Army A-22 Cargo Container.
1.1 A-22 Container and Standard Aerial Delivery System
A description of the A-22 Container with illustrations
is given in the Department of the Army Technical Manual TM-530
of June, 1952, (Ref 1). This manual was provided by the
Procuring Agency together with drawings of the component parts
of the container, namely the sling, inner liner, skid, and
web. Appendix l11c, p 46 of Ref 1 lists the suggested loads
and main dimensions of typical cargo for the A-22 Container.
The maximum dimensions for the base are 52 in. x 43 in. and
the height varies between 60 in. (max) and 40 in. (min). The
A-22 Container was designed for delivery by the floor level
roller conveyor system using the G-12D parachute. This is a
64 ft diameter, flat circular parachute with the following
characteriotlos (P14r 2, p 2-1-3):
Rated Weight Capacity 2,200 lbs
CDo 0.75
Angle of Oscillation 300 (approx)
Air Drop Speed Limit 175 knots
Rate of Descent 27.6 ft/sec(with 2,200 lbs load)
Weight 126 lbs
Manuscript released by the authors on July, 1961, for publicationas an ASD Technical Report.
ASD TR 61-326 1
1.2 High Velocity Aerial Delivery
Recent trends in the aerial delivery of cargo require
much higher rates of descent, of the order of 75 ft per second
or more, together with more stringent stability requirements
and the use of energy dissipating, cushioning devices at ground
impact. Reference 3 shows that by using a 22 ft ringslot para-
chute giving a rate of descent of about 75 ft per second,
together with paperboard honeycomb as cushioning material, the
following advantages could be achieved:
1) Greater drop accuracy
2) Reduced dispersion due to wind effects
3) Considerable reduction in the cost of aerial
delivery.
To assure a high degree of efficiency of this system, the longi-
tudinal axis of the parachute load system shall not deviate
more than five degrees from the tangent of the ballistic tra-
jectory. The main objective of this study is to determine the
type and size of a parachute which would fulfil. this require-
ment with q minimum amourt- of pa.a.hu.e drag,
II. EXPERIMENTAL EQUIPMENT
2.1 Wind Tunnel
The experimental tests were conducted in the open test
section arranged in the return circuit of the University of
Minnesota subsonic wind tunnel. Figure 1 is a schematic layout
of this tunnel giving its main dimensions and indicating the
modifications introduced in the return circuit of the wind
2
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tunnel to provide an open test section (Free Jet). Figure 2 is
a photograph showing the honeycomb and contraction sections
upstream of the open test section.
2.2 Model Mounting Frame
A special frame for mounting the A-22 Container and
parachute models was built and is illustrated in Fig 3. When
mounted in this frame, the A-22 Container model is free to
rotate about an axis perpendicular to the air stream. The
design of the frame is such that the pivotal axis may be set
vertically (as shown in Fig 3A) or horizontally (Fig 3B). In
the vertical mounting position, gravity effects on the container
may be neglected and only the aerodynamic forces and moments
will be effective. The vertical mounting position was used
in all tests reported here and Fig 4 illustrates with main
dimensions the general layout of the model and mounting frame
in the open test section.
The 3/8 inch diameter pivotal shaft incorporates two
strain gage balances for moment and drag measurement. The
lYwt-r PrO jf the pivotal shall could be attached to the rotating
arm of a wire wound potentiometer for recording the instan-
taneous angular position. In addition, means were provided
for locking the pivotal shaft in any position; this was used
when recording the moment on the container model alone and the
container and parachute models in combination.
The A-22 Container models, the parachute models, the
moment and force balances, and the angle measuring devices
are described in the following paragraphs.
-4-
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1 L.
0z
x4I (LU
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07La0
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I Li
/w
*1 R L
QkN
w"I-N Or 2Z2
CARGO CONTAINER
OPEN TEST SECTION
PARACHUTE
442"
SCALE= 1:24
DIMENSIONS IN INCHES
FIG. 4-GENERAL LAYOUT OF MODEL. IN WIND
TUNNEL
-7-
A-22 Container Models
Each container model has a central brass fitting into
which the two halves of the pivotal shaft can be fitted and
anchored as shown in Fig 5.
Orthogonal to the pivotal shaft is a steel threaded
shaft which holds steel plates, representing the container base
and top. The plates can be arranged at various distances to
each other to represent various container heights and various
relative positions of the pivotal axis with respect to the top
and bottom faces of the container which measure simulates
different center of gravity locations of the container. Figure
5 shows design details of the 1/6 scale A-22 Container model.
2.4 Parachute Models
The experimental tests involved parachute canopy models
of the following types:
1) Solid flat canopy
2) Ring slot, 20% porosity canopy
3) Ribbon, 20% porosity canopy
4) Ribless guide surface canopy.
The first type (solid flat) was used for purposes of comparison
and reference,
The parachute model specifications are given in Fig 6.
(See page I0)
-4-
fiiI I
I - 10 --
IIIIi II
, If ,I ifj, ,, l22
' 2
S 2
SCALE- 1:4
DIMENSIONS IN INCHES
FIG. 5- DETAILS OF 1/6 SCALE A-22 CONTAINERMODEL FRAME
-9-
L = length of suspension lines; Dp = projected diameter; Do
ominal diameter; S= projected area; So = cloth area; and
W = parachute model weight.
MODEL TYPE L (in.) DpOn.) Do (in.) Sp(f t2 ) S. (f t ) W (oz
Solid Flat 16.0 - - 16.0 - - 1.452 0.854
Ring Slot, 20% Poro-sity, 100" prototype 16.5 - - 16.0 - - 1.396 1.119
Ribbon, 20% Porosity100" prototype 17.0 - - 16.o 1.396 1.244
Ribless Guide Surface 16.0 11.84 - - 0.765 - - 0.620
FIG. 6- PARACHUTE MODEL SPECIFICATIONS.
2.1=e geofii't!iLcally oiwila ± models o the A-22 Container
were used in conjunotion with a single parachute model of each
type. This procedure was preferred to the other alternative of
using one container model and three parachute sizes, since
container models are less expensive and easier to manufacture
than parachute models. Furthermore, the use of parachute
models of different sizes would involve dynamic behavior such
as natural frequency, period of oscillation, parachute weight,
-10-
etc., which might complicate the analysis. On the basis of the
three scales of 1/8, 1/6, and 1/4 and the model parachutes used,
as specified in Fig 6 the corresponding full scale parachutes
would have projected diameters, Dp, of 96, 72, and 48 in.,
respectively, for the ribless guide surface and flat diameters,
D o , of 128, 96, and 64 in. for the solid flat, ribbon, and ring
slot parachutes. These relative sizes are also presented in
Fig 7.
MODEL CONTAINER SCALE
1/4 1/6 1/8Solid Flat, Do (in.) 64 96 128
Ring Slot, Do (in.) 64 96 128
Ribbon, DQ 64 96 128
Ribless Guide Surface, DP (in.) 48 72 96
FIG. 7- FULL SCALE PARACHUTE DIAMETERS CORRESPONDING TOTHE PARACHUTE MODELS AND DIFFERENT SCALE CONTAINERS
Figure 8 illustrates a container parachute combination
in 1/78 .n... ..parachut 96 in. diauier) ana tne 1/4
and 1/6 scale container models.
The designation by scale is an indirect way of indicating
the size of parachute corresponding to the A-22 Container; this
is obtained by dividing the parachute model diameter by the
scale factor.
The scale was a convenient way of setting up the
experiments and classifying the results; however, to make the
-11-
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1 )
w z
Ll
-12-0
= I
presentation of results of more immediate physical significance,
we will present the test results in terms of the full scale
parachute diameters corresponding to each test configuration.
2.5 Strain Gage Moment Balance
An earlier design of a moment balance proved unsatis-
factory, and a different design using the torque tube principle
was then constructed and calibrated. The general arrangement
and main details of the moment balance are illustrated in Fig 9.
The upper end of the lower half of the 3/8 in. diameter
pivotal shaft was drilled out to a wall thickness of 0.030 in.
and a depth of 2.75 in., and a 0.75 In. long steel plug was
driven into the drilled rod to seal off the end and form a
hollow section 2 in. long to serve as the torque tube. Four
Baldwin SR-4 type A-7 strain gages were cemented to the tubular
section along two orthogonal but not intersecting helical paths
on the surface of the torque tube and connected as a 4-arm
bridge circuit.
The pivot shaft was then remounted in bearings on the
test frame with tho torque tube end pa!sing Into tb'c brass
fitting of the model container and locked in place with two
set screws. The strain gages are thus located inside the
container model where they are protected from mechanical
damage.
Figure 10 illustrates the calibration curve of the
moment balance.
2.6 Strain GageDrag Balance
A strain gage drag balance was constructed as an integral
-13-
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<H
LL 0
0 L 0
o Lii
00M U
L1 -JIL< 0
-- ~~~L C) () L.
LL2 2
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__ 0
00
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Z 2
-c - Hzz
10 0F
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'NI -NO1.~1330
part of the upper section of the pivotal shaft. For this purpose,
the end of the pivotal shaft which fits into the brass fitting
within the container model was drilled to a depth of 2.75 in.
leaving a wall thickness of 0.040 in. Strain gages were then
cemented along the axis of the shaft, two on each side of the
hollowed section, and the four strain gages were electrically
connected as a 4-arm bridge. The pivot shaft was then re-
installed on the test fram with t1fe drag balance end passing
into the container brass fitting and secured with set screws.
The general arrangement of the drag balance and its main
dimensions are illustrated in Fig 9, and its calibration curve
is presented in Fig 11.
Z.I Attitude Measuring Devices
.7.1 Container Angle Measuring Device
The device is essentially a wire wound potentiometer
mounted at the lower end of the pivotal shaft with the potentio-
meter wiper locked to the pivotal shaft to record the instan-
taneous angular position of the container's longitudinal axis
with respect to the air stream.
The potentiometer has 1020 turns over an arc of 340
degrees, i.e., the angular resolution is 1/3 of 1 degree. The
potentiometer was connected in a two-arm bridge circuit.
Figure 12 gives the static calibration curve which indicates
satisfactory sensitivity and linearity.
2 Parachute Angles Measuring Device
A special device for measuring the parachute attitude
- C--
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0-I-iw---- \ --.--
N
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z0
00 -
o
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0 U0
' N I - N0110I~3143
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_ 4_
zz_ o
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0H
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0-~ U
(Nl
0(9
angles was constructed and is illustrated in Figs 13 and 14.
It has, on one side, a rigid cross frame with four
pick-up points which are hinged to the four lines forming the
A-22 Container model suspension web (spider) and on the other
side, an axial arm which engages the clevis assembly of the
parachute model.
This attitude measuring device provides free pivoting
about two orthogonnal ax s and, when the device is in its neutral
position, i.e., when the longitudinal axis of the container and
that of the parachute coincide with the direction of airflow,
the pivoting axes are respectively horizontal and vertical and
both lie in a plane perpendicular to the direction of airflow.
The angular motions about each of these two axes are
transmitted to the wipers of two miniature potentiometers.
Each potentiometer forms the variable arms of a two-arm bridge
circuit. One of the potentiometers picks up the angle of yaw
(Angle 0) while the other is sensitive to the angle of pitch
(Angle *) of the parachute axis with respect to the container's
longitudinal axis.
Calibration of the two miniature potentiometers is
given in Figs 15 and 16. These potentiometers have a carbon
ring as the resistance element and, because of the severe
limitations of size, their linearity is not as good as that of
the large wire-wound type used on the container pivotal axis
but it is acceptable.
2.8 Parachute Risers
Initial tests to determine the moment coefficients and
-19-
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Fif~.,re 13. ]%racht e Attitude Measring Device
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-23-
the free attitude angles were conducted without risers.
In actual aerial delivery, a riser is interposed bet-
ween the container spider web and the parachute suspension
lines. Tests representing the 72 in. and 48 in. guide surface
parachutes and the 96 in. and 64 in. solid flat, ribbon, and
ring slot parachutes were conducted with various riser lengths
up to and Including scaled riser lengths representing 30 ft
full scale.
III. EXPERIMENTAL PROCEDURE AND RESULTS
3.1 System of Reference
It is convenient to specify a system of three orthogonal
axes with its origin at the C. G. position of the container.
The first axis, the longitudinal axis, may be defined as the
axis through the C. G. perpendicular to the base of the con-
tainer, i.e., in the height direction. The other two axes
through the C. G., the lateral axes, are orthogonal to the
longitudinal axis. One may consider an infinite number of such
orthogonal lateral axes but, since the spider web attaches at
the mid-points of the rectangle forming the top surface, it is
natural to consider the system of two lateral axes that are
perpendicular to the side faces of the container. Figure 17
illustrates the reference system used, gives the notation for
the container, and parachute attitude angles, and indicates
the critical orientation for the pivotal axis, the reference
area, and the characteristic length used in the aerodynamic
calculations.
-24-
NOTATION FOR CON- TOP VI EWTAINER AND PARACHUTEATTITUDE ANGLES8
slu VIEW
PARACHUTE
MEASRINGPARACHUTE SUS-DIVICEPENSION LINES
PIVOTAL AXIS FORRE-ORIENTATED POSITION
AXIS >---ATTACHMENT POINTS
____NPIVOTAL AXIS FOR ORIGINALFLC'OR10IENTATION (CRITICAL CONFIGURATION)
CONTAINER BASE AREA43' - 5 2 x - 2 2 3 6 fla (REF.AREA)
BASE DIAGODNAL67.48 in (CHARACT. LENGTH)
FIG. 17 SYSTEM OF REFERENCE
-25-
3.2 Test Reynolds Numbers
All the tests presented in this report were conducted
at a dynamic pressure setting of q = 5.20 lb per sq ft corres-
ponding to an air speed of 67.6 ft per sec and a water head of
1 inch. Throughout the testing, the pressure head was accurately
controlled by means of a Meriam Micromanometer with a sensitivity
of 0.001 inch of water.
The reference area used for calculating the aerodynamic
coefficients was the container base area and the characteristic
length used for calculating the moment coefficient and the
Reynolds number was the diagonal of the container base. On
the basis of this characteristic length and the other experi-
mental conditions, the corresponding Reynolds numbers for the
different scales were as follows:
Re = 2.75 x 105 for the 1/8 scale container
Re = 3.66 x 105 for the 1/6 scale container
Re = 5.49 x 105 for the 1/4 scale container.
Critical Container Configurations
3 Critical Container Orientation
Since the container base is not square but rectangular,
it was necessary to determine the critical container orientation,
i.e., the one producing the largest de-stabilizing moments.
For this purpose, tests were conducted with the 1/6 scale con-
tainer model mounted on the test frame in the two possible
oriontations and the moments were measured through the full
range of angles.
-26-
The results are illustrated in Fig 18 from which it is
seen that the original position is the more critical and this
orientation was therefore used for all subsequent tests.
3.3. Critical Container Height
Since the container height is variable, depending on the
nature of the load, tests were conducted with container models
representing the two extreme values of the height corresponding
to maximum and minimum heights (respectively 60 and 40 inches
full scale). Figure 19 gives the result of these tests indicating
that the maximum height configuration has the more critical
stabilization requirements, i.e., smaller stable range and
stable moment coefficients in that range and larger de-stabilizing
moments beyond it. The maximum height configuration was there-
fore used in all the later tests.
3.4 Tests with Container Model Alone
3.4.1 Moment Characteristics
Each of the three container models (1/8, 1/6, and 1/4
scale) was successively mounted on the test frame, statically
balanced, and carefully positioned. The zero angle of attack
was selected at the position where Lhe resulting galvanometer
deflection, i.e., the moment coefficient was zero. This adjust-
ment was necessary because the airflow is slightly non-symmetrical
in the secondary test section of the wind tunnel. The moments
were then recorded in two degree increments for a in the range
from 0 to + 20 degrees and in five degree increments from + 20
to + 90 degrees.
-27-
0
0 U)
t:- o 3
o -z
F- -1 0!LL
ZN _L Le) -L!_ D cc
/<
Uk .of Z
L~ L CdCUJ~2~
0'0L 4 0 k
0
I z0
2!La
ZUJZ
0-
-28-
Q0
Ldz
zL=1
2 -0 0
z.
JL za
_ IX~ LI)
z7ZL< 0 -
-LJl
0 0Q0
z
0 15": -J Q) 0
LA- iiV 0
0 0-j IL
-29-
The moment coefficient versus the angle of attack for
the three scale container models alone are presented in Fig 20.
This figure indicates that the container alone is stable in a
range of about + 25 degrees. Beyond that range, it is unstable.
Comparison of the moment coefficients for the three
geometrically similar scale models of the container indicate the
same general shape for the variation of moment coefficient with
angle of attack, but with small differences in the numerical
values.
Tests with Parachute Stabilized Container Model
Without Risers
3.5.1 Moment Characteristics
After testing each scale model of the container alone,
the attitude measuring device was secured to the container web,
a parachute model was attached and the system statically
rebalanced. The moment characteristics for the system were then
recorded in two degree increments for a in the range from 0 to
+ 20 degrees and in five degree increments beyond ± 20 degrees.
These were repeated for each of the four parachute models
listed in Fig 6.
For the configurations representing guide surface para-
chutes of 96 in. and 72 in. diameter and parachutes of 128 in.
and 96 in. for the other three types, the angular range without
risers was limited to + 45 degrees.
For the configurations representing a 48 in. guide
surface parachute and 64 in solid flat, ribbon, and ring slot
-30-
_ _ __ __LL
0
U99
0 LLZ
LLco R zdw
z
00
IT0
LEL-31.A
parachutes, it was not practical to go beyond a + ± 35 degrees
because of the violent parachute motions resulting from the
large wake and the fact that some of the spider web lines
became slack at large angles.
In all cases, the values obtained for the moment
coefficients at identical positive and negative angles of
attack were averaged to account for minor flow variations in
the test section.
3.5.1.1 Tests with Parachute Models Representing Solid
Flat, Ribbon, and Ring Slot Parachutes of 128 inch
Diameter and a Ribless Guide Surface Parachute of
96 inch Diameter
Figure 21-A, B, C, and D present the moment coefficients
for the A-22 Container in combination with the four parachute
types with no risers.
Figure 21-A shows the moment characteristics for the
parachute container configuration representing a solid flat
parachute of 128 inch diameter. This configuration exhibits
an unstable range of + 6 degrees, beyond which it is stable
up to the maximum range tested (± 40 degrees). Furthermore,
the maximum moment coefficient (1.37 at 40 degrees) was the
highest of the four configurations tested.
Figure 21-B shows the moment characteristics for the
configuration with a 20% porosity 128 inch diameter ring slot
parachute it exhibits an unstable range of + 4 degrees, beyond
which it is stable up to the maximum range tested (± 45 degrees).
The maximum measured value of the moment coefficient was 1.12 at
45 degrees.
-32-
61- ~I -1
-33
Figure 21-C gives the moment characteristics for a para-
chute container system using a 20% porosity 128 inch diameter
ribbon parachute. It indicates that this configuration is stable
over the full angular range tested, i.e., + 45 degrees. The
maximum stabilizing moment coefficient measured was 0.93 at
45 degrees.
Figure 21-D indicates that a 96 inch diameter ribless
guide surface parachute would stabilize the container over the
full range tested, i.e., + 45 degrees. The maximum stabilizing
moment coefficient measured was 0.96 at 45 degrees.
Figure 22 presents, for comparison purposes, the moment
coefficient versus a for each of the four parachute container
configurations given above when used with no risers.
3.5.1.2 Tests with Parachute Models Representing Ribbon
and Ring Slot Parachutes of 96 inch Diameter and a
Ribless Guide Surface Parachute of 72 inch Diameter
The moment characteristics for the container parachute
configuration with the 20% porosity, 96 inch diameter ring slot
parachute are shown in Fig 23-A. This combination in f :'na ;J
be uiab±e for all angles of attack tested. The maximum moment
coefficient was obtained at + 25 degrees, the value being 0.345.
This combination had the greatest stabilizing characteristics
of the types tested in the region near a = 0.
Figure 23-B shows the moment coefficients for the con-
tainer in combination with the 20% porosity, 96 in. diameter
ribbon parachute. This configuration is stable for all measured
angles of attack. The maximum moment coefficient was 0.240 at
-34-
ci~
z~ (D,
Lo
z LLCJ
ZL')ZV)N
zLO T -
a 00 V0
ILL01z
\L~ -i 2
0 0
m W
d
-36
an angle of attack of + 25 degrees. For this configuration,
(dCm/da).= 0 was less than the value for the ring slot com-
bination.
The moment coefficients for the container with the 72 inch
diameter ribless guide surface parachute are presented in Fig 23-C.
This plot reveals that the configuration is stable for all angles
in the region tested. This combination has the smallest (dCm/da)a=
of the three configurations tested.
Figure 24 presents, for comparison purposes, the moment
coefficient versus a for the ring slot, ribbon, and ribless
guide surface parachute container configurations given above
when used with no risers.
3.5.1.3 Tests with Parachute Models Representing Solid
Flat, Ribbon, and Ring Slot Parachutes of 64 inch
Diameter and a Ribless Guide Surface Parachute of
48 inch diameter
Figure 25-A shows the moment characteristics for a system
with a 611 inch diameter solid flat parachute attached to the
A-22 Container with no risers. It indicates a stable configuration
over the range tested (+ 35 degrees). The maximum stable moment
coefficient was CM = 0.145 at 18.5 degrees. In addition, this
combination appeared to have the largest value of (dCm/da )a= O'
Figure 25-B indicates that a 20% porosity 64 inch dia-
meter ring slot parachute attached to the container with no
risers gives a stable configuration over the range tested
( 30 degrees). This combination has a maximum stable moment
coefficient CM = 0.082 at 15 degrees, and the slope of the
-37-
In zC) ) 1. z
Q~0) 000 az
0j ' C\j L-
000
LU-
07.
LO 0 LJQ0LnLMi5
,fgo
/P
qi 4 - 4
ca ~-2
sZ.
K1-14
Qw
moment coefficient curve at zero angle of attack is larger than
for either the guide surface or ribbon combinations.
Figure 25-C shows the moment coefficient versus the angle
of attack for the 20% porosity 64 inch diameter ribbon parachute
container configuration with no risers. This configuration is
stable over the range a= ± 32 degrees, and the maximum
stable moment coefficient measured was 0.074 at a= 14 degrees.
The value (dCm/da) . = 0 is very small.
Figure 25-D indicates that a 48 inch diameter ribless
guide surface parachute attached to the container with no risers
produces a stable configuration over the range a = _+ 36 degrees.
The maximum stable moment coefficient measured was 0.09 at a=
16 degrees. The slope of the moment coefficient curve at zero
angle of attack (dCm/da ) a= 0 is very small.
Figure 26 presents, for comparison purposes, the moment
coefficient versus a for each of the four parachute container
combinations listed above with no risers.
3.5.2 Drag Characteristics
The experimental values of thf draf, cocffllciv,,U for
the container alone and the system drag when the container is
set at a = 0 for each of the three scale midels in conjunction
with the four parachute types without risers are given in Fig 27
and illustrated in Fig 28. The drag forces were measured by
means of the strain gage drag balance incorporated in the verti-
cally mounted container pivotal shaft and described in Paragraph
2.6. Drag measurements were not originally enviiaged but were
deemed very desirable for comparison of the relative merits of
-40-
z< cnWl$
0
(V) [LJ rZ
Z )
U Ln)zC\Z0
oiUd z
--. 0 0 og W(t)
=) *"q - L
LLJ Cl LLJ
0 13 -LL1-
AVERAGE DRAG COEFFICIENT AND FULLSCALE PARACHUTE DIAMETER
V8 SCALE SCALE h4 SCALE
CONTAINER ALONE CD 0.802 0.950 o.8o
CONTAINER AND SOLID Cp 5.509 - - - 1.507FLAT PARACHUTE D0 128 IN. 64 IN.
CONTAINER AND RING C 3.930 2.660 1.170
SLOT PARACHUTE Do 128 IN. 96 IN. 64 IN.
CONTAINER AND RIBLESS 3.690 2.550 1.230GUIDE SURFACE D 8PARACHUTE p 96 IN. 72 IN. 48 IN.
CONTAINER AND D 3.530 2.380 1.160RIBBON PARACHUTE D 128 IN. 96 IN. 64 IN.
FIG. 27-AVERAGE DRAG COEFFICIENTS BASED ON CONTAINER BASE AREAFOR VARIOUS SCALE CONTAINER-PARACHUTE COMBINATIONS WITH NO RISERS
6
H H H
oo4II U cQ 1 DRAG COEFFICIENT FORI CONTAINER ONLY
4 0- -- _ _ _ _ _ __t.OOC'J OI' ccQ
II'111D2
II:i- A HH
0~ -4 01 -410 P n
A _E- o0 E- 0
o E 0 O
k/l CI
I"W Q r4 m II
0 . ro I
% SCALE -1 SCALE -1 -- I4 SCALE --4
FIG. 28- DRAG COEFFICIENTS FOR VARIOUS CONTAINER - PARACHUTECOMBINATIONS. CONTAINER BASE REFERENCE AREA- 15.53 FTZ
-42-
the different parachutes and the selection of an optimum type.
The drag coefficients presented in Fig 28 are all cal-
culated with the container base area, namely 15.53 ft2 full
scale, as reference, and this explains the reason why the numeri-
cal values are very large, particularly for the cases representing
the largest parachute namely, 128 in. for the solid flat, ribbon
and ring slot parachutes and 96 in. for the ribless guide
surface type. Figure 28 shows that, for the cases of the
smallest parachutes represented, namely 64 in. for the solid
flat, ribbon and ring slot and 48 in. for the ribless guide
surface, the additional drag due to the parachutes is but a
small fraction of the drag of the container alone. This drag
represents a 44% increase for the ribbon parachute case, a 46%
increase for the ring slot parachute, a 53% increase for the
ribless guide surface parachute, and an 87% increase for the
solid flat parachute.
It is significant that the total drag coefficient with
the ribless guide surface parachute is higher than that with
the ribbon parachute for all container scales.
Parachute and Container Free Attitude Angles
After recording the moment and drag characteristics,
the locking arrangement on the pivotal shaft was released, the
container angular measuring device and the parachute attitude
measuring device were activated, and the free angles a , e ,
and * for the four types of parachutes in conjunction with
different scale containers were recorded These tests were
made with no risers between the container spider web and the
-43-
parachute suspension lines. Figures 29-A, B, and C are photographs
of the experimental arrangement of the 1/4 scale container in
combination with parachutes representing full scale diameters
of 64 in. for the ringlsot and ribbon types and 48 in. for the
ribless guide surface parachute with no risers.
From a visual observation of the behavior of the freely
suspended container and parachute models for different parachute
types and container scales, the following qualitative remarks
can be made.
The solid flat parachute (Fig 30-A) exhibited very
large amplitude random motion and violent oscillations for all
container scales. This parachute appeared to be the least suit-
able for stabilization of the A-22 Container. The ring slot
parachute model (Fig 30-B) exhibited some oscillation of the
parachute about the container's longitudinal axis for the
different configurations but was decidedly more suitable than
the solid flat type. The oscillations of the container about
its pivotal axis and the random motions of the parachute axis
appeared to be much smaller for thc ribbon parachute model In
ito variou6 .viifiguratlons (Fig 30-C). The various configurations
using the ribless guide surface parachute model appeared to
exhibit the smallest departures in container axis angle a and
parachute mean attitude angles 8 and * from the axial flow
direction, although the frequency of oscillation of the con-
tainer and parachute model was higher than that of the other
types (Fig 30-D). Both the ribbon and the ribless guide surface
parachutes appeared to be quite satisfactory for stabilizing the
A-22 Container.
-44-
iii' A MODEL ARRANGEMENTREPRESENTING CONTAINERAND 20Olo POROSITY 64" DIA.RING SLOT PARACHUTE
. _ 'B. MODEL ARRANGEMENTREPRESENTING CONTAINERAND 2Oo/o POROSITY 64DIA. RIBBON PARACHUTE
M.DEL ARRANGEMENTREPRESENTING CONTAINERAND 48* DIA. RIBLESS GUIDESURFACE PARACHUTE
FIG. 29-EXPERIMENTAL ARRANGEMENT OF THE 1/4 SCALE A-22CONTAINER IN COMBINATION WITH THREE PARACHUTE TYPESWITH NO RISERS
- 5-
S. 'an1mwtaf1wu slM~f 41 /-
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COWIAT IP 55ACMI AMR.5 AN6 o AMD SI YM I. 7/f t .. i.7r
-46
In our experimental arrangement, the parachute models
are suspended horizontally behind the container model in the
test section and the weight of the parachute tends to produce
a positive attitude angle 4' which depends on the parachute
model weight, the aerodynamic forces involved, and the riser
length. For this reason, the angle 4 as measured is not
representative of actual aerial delivery conditions where the
path is more nearly vertical for most of the trajectory after
full deployment. Therefore, the recorded angles ' are not
illustrated.
3.6 Tests with Parachute Stabilized Container Models
with Risers
Since risers are invariably used in aerial delivery,
a series of tests with scaled down riser lengths corresponding
to 10, 20, and 30 ft were carried out. These tests included
recording the moment characteristics, the system drag at zero
container angle of attack, and the free attitude angles- They
involved parachute container configurations representing full
scale parachute diameters of 96 in. and 64 in. for the ribbon
and ring slot parachutes and 72 in. and 48 in. for the ribless
guide surface type.
3.6.1 Moment Characteristics
3.6.1.1 Tests representing 96 in. Ribbon and Ring Slot
Parachutes and a 72 in.Ribless Guide Surface Parachute
In practically all tests with risers, the full angular
range of + 90 degrees was used and the values obtained for the
-47-
moment coefficients at identical positive and negative angles
of attack were averaged to account for minor flow variations
in the test section. To limit the number of experimental tests
arid data points to a reasonable amount, we conducted no moment
tests with risers with the solid flat parachute container com-
bination. Tests without risers had established the relative
inferiority of this type of parachute in comparison with the
other three types.
Figures 31-A, B, and C illustrate the variation of the
moment coefficients with the container angle of attack for the
96 in. diameter ring slot and ribbon and the 72 in. diameter
ribless guide surface parachute container configurations without
risers and with risers representing 10, 20, and 30 ft length in
full scale.
It is apparent that the use of risers considerably
increases the stabilizing moment coefficient particularly at
large container angles.
It is also significant that, except for the ribbon para-
chute at large angles a , relatively little changes of Cm occur
for increased riser lengths beyond 10 ft suggesting that other
things being equal, a 10 ft riser would be adequate for this
configuration.
Figures 32-A, B, and C present, for comparison purposes,
the moment coefficients for the 96 in. ring slot and ribbon
and the 72 in. ribless guide surface parachute when used with
risers representing 10, 20, and 30 ft full scale respectively.
Figure 32-A shows that for a 10 ft riser length, the ring slot
-48-
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AND A'kcR IEN6114; A A&Ipf
-50-
parachute configuration has a small unstable range of ± 5
degrees and the largest stabilizing moment coefficients at
large angles of attack.
The ribbon parachute configuration has the largest
moment coefficient slope at zero angle of attack (dCm/da) a= 0
of the three types tested, while the ribless guide surface has
a very small value of (dCm/da ) a= . and a smaller value of
the moment coefficient over practically the full angular range.
Figure 32-B indicates that for a 20 ft riser length the
ring slot and ribbon parachute configurations have nearly the
same moment coefficients over the full angular range while the
ribless guide surface container combination has smaller Cm
values over practically the entire angular range.
Similar conclusions can be drawn from Fig 32-C for a
30 ft full scale riser length.
3.6.1.2 Tests Representing 64 in. Ribbon and Ring Slot
Parachutes and a 48 in. Ribless Guide Surface Parachute
Figures 33-A, B, and C show the variation of the moment
coefficients with the container angle of attack for the 64. in.
ring slot and ribbon parachutes and the 48 In. r.bless guide
surface parachute configurations without risers and with risers
representing 10, 20, and 30 ft lengths in full scale.
It is apparent from Figs 33-A, B, and C that the use of
risers considerably improves the stabilizing characteristics
and produces a stable configuration over the full angular range
of + 90 degrees Instead of a limited angular range of about
+ 35 degrees for the cases without risers.
-51-
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-52-
For the 64 in. ring slot container configuration, Fig 33-A
indicates that a 20 ft riser produces larger stabilizing moment
coefficients over the full angular range than either the 10 ft
or 30 ft risers.
Figure 33-B shows that the 64 in. ribbon parachute con-
tainer combination without risers is unstable beyond a = 33
degrees. The use of risers stabilizes this configuration over
the full angular range. The 20 and 30 ft risers produce sub-
stantially the same stable moment coefficients over a large part
of the angular range and these coefficients are appreciably
larger than those with a 10 ft riser.
Figure 33-C shows that the 48 in. ribless guide surface
parachute container combination is unstable beyond a = 35.5
degrees. The use of risers, however, produces stable moment
coefficients over the full angular range. For this configuration,
it was not possible to test with the 30 ft riser or to carry
the 20 ft riser case beyond 45 degrees. This was due to the
particular character of the flow in the open test section which
produced a secondary flow that carried the ve2y light parachute
model outside the test section. This condition is peculiar to
the testing arrangement and would not be reflected in full
scale, free flight.
Figures 34-A, B, and C present, for comparison purposes,
the moment coefficients for the 64 in. ring slot and ribbon and
the 48 in. ribless guide surface parachute modcls when used in
conjunction with the A-22 container with risers representing 10,
20, and 30 ft full scale respectively.
-53-
1- Pill 1111 1 m
till I III H ill 1! lili I'll 1;;; 11 liv
'll ION 1111Ill
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itpit
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COEFflelevr FoR YARIOVC, PARA Ct 1417Z - CONI'AIMER
coMJ31A(A TIONS AMD A116ER 1,6WC, 7"6- Re -,!F:49 /Ox 7 -1.20 zalsg. Rr.
-54-
Figure 34-A shows tha.t, for the 10 ft riser case, the
64 in. ribbon and the 48 in. ribless guide surface parachute
configurations have substantLally the same moment coefficients
over most of the range while the 64 in. ring slot conflguration
has considerably larger moment coefficients over the full angular
range.
For the 20 ft riser c-ase, Fig 34-B indicates the stable
moment coefficients to be largest for the 64 in. ring slot
parachute, smallest for the 4C in. ribless guide surface para-
chute, and intermediate for thie 64 in. ribbon parachute.
3.6.2 Drag Characteristics
3.6.2.1 Tests Representing 96 in. Ribbon and Ring Slot
Parachutes and 72 in. Ribless Guide Surface Parachutes
Figures 35-A, B, and C present the individual drag
coefficients of the container and the parachute as well as the
drag coefficients of the combination or system drag for the A-22
Container with the 96 in. ring slot and ribbon and the 72 in.
ribless guide su-rface parachutes for riser lengths of 10, 20P,
and 30 ft. In all cases, the drag coefficients are based on
the container base area and tis explains why the drag coeffi-
cients of the container alone and the parachute alone are also
plotted for comparison with the system drag.
The drag coefficients of the parachutes alone steadily
decrease with increasing riser length. This is mainly due to
the fact that the flow downstream of the contraction in the free
jet is not uniform and there eists a velocity gradient in the
longitudinal direction. However, the differences are quite
-55-
II
0u
o 0
5
4
ot
small, particularily for riser lengths representing 20 ft or less.
Figure 35-A shows that, for the 96 in. ring slot para-
chute container configuration, the system drag coefficient is
increased 'by about 15% by using a 10 ft riser. For this case,
the system drag coefficient is substantially equal to the sum
of the drag coefficients of the container and parachute models
taken separately. There is a very slight reduction of system
drag coefflcient for the 20 ft riser and an appreciable reduction
for the 30 ft riser case. This appears to be largely due to
the longitudinal velocity gradient.
Figure 35-B for the 96 in. ribbon parachute container
configuration indicates that the system drag coefficient is
maximum for the 30 ft riser but the absolute values are somewhat
smaller than the ring slot case, and the system drag is, for
all riser Lengths, smaller than the sum of the drag of the
individual container and parachute.
Figure 35-0 for the 72 in. ribless guide surface para-
chute container configuration shows that the use of a 10 ft
riser produces only a small increase of system drag (about 4%).
For risers of 20 and 30 ft. the system drag coefficients decrease
far more than would be expected from the decrease of drag
coefficient of the parachute alone. The reason for this effect
could not be ascertained.
Figure 36 shows, for comparison, the system drag
coefficient for the A-22 Container stabilized by the 96 in.
ring slot and ribbon parachutes and the 72 in. ribless guide
surface parachute using risers of 0, lO, 20, and 30 ft.
-57-
70
0 8
-1---
-58-
It is apparent that, for the same riser length, the system drag
is appreciably larger for the configuration employing the ring
slot parachute, while the ribbon and ribless guide surface
parachutes produce substantially the same drag for riser lengths
of 0, 10, and 20 ft. For a riser of 30 ft, however, the ribbon
parachute produces an appreciably larger system drag coefficient
CDs = 2.81 compared to CDs = 2.31 for the ribbon guide surface
case.
3.6.2.2 Tests Representing 64 in. Ribbon and Ring Slot
Parachutes and 48 in. Ribless Guide Surface Parachute
Figures 37-A, B, and C present the individual drag
coefficients of the container and the parachute as well as the
system drag coefficients for the container with the 64 in. ring
slot and ribbon parachutes and the 48 in. ribless guide surface
parachute for riser lengths of 0, 10, 20, and 30 ft full scale.
The summation of the individual drag coefficients of the con-
tainer and parachute is also plotted in these figures for com-
parison with the system drag.
Figure 37-A shows that for the 64 in. ring slot parachute
container configuration, the use of a riser produces a considerable
increase of drag coefficient. With no risers, the system drag
coefficient is 1.17; with a 10 ft riser, the drag coefficient
is increased to 1.89 and reaches a maximum value of 2.05 for
a 20 ft riser and then is reduced to 1.80 for a 30 ft riser.
It is significant that for this configuration, the system drag
coefficient is larger than the sum of the individual drag
coefficients for all cases using risers.
-59-
G-~
dy q
e 0
I0 0
ao
_ 8
-- ti (-Iz
00
0
II
_ _L I 4
II 0
-6o-
Figure 37-B for the 64 in. ribbon parachute container
configuration shows that the system drag coefficient without
risers CD = 1.16; this increases to CD = 1.77 for a 10 ft
riser, D= 1.80 for a 20 ft riser, and CD, = 1.87 for a 30 ft
riser. Again, it is noted that the system drag coefficient
CDs is larger than the sum of the individual drag coefficients
CDp + for all cases using risers.
Figure 37-C for the 48 in. ribless guide surface parachute
container configuration shows a system drag coefficient CDs =
1.23 without risers, increasing to 1.65 for a 10 ft and a 20 ft
riser. For this configuration, the system drag coefficient is
again found to be larger than the sum of the individual drag
coefficients although the difference is much smaller than the
ribbon or ring slot configurations.
It would appear from Figs 37-A, B, and C that with the
relatively large container and correspondingly large wake, a
positive "interference effect" takes place resulting in greater
system drag coefficient than the sum of the individual drag
coefficients. This is not the case for the previous tests
where the interference effect was negative, i.e., producing a
system drag coefficient smaller than the sum of the individual
drag coefficients.
Figure 38 shows, for comparison, the system drag co-
efficient for the A-22 Container stabilized by the 64 in. ring
slot and ribbon parachutes, and the 48 in. ribless guide surface
parachute using risers of 0, 10, 20, and 30 ft. It is apparent
-61-
I zI Ld
LUL
i2 LA
.
o 2
0~ ~ 0 o~V )
z HZ-j z
cr LiLL±Jc
-- 0-----SoUZ
that for the same riser length, the system drag coefficient is
larger for the ring slot parachute container configuration than
either the ribbon or ribless guide surface configurations for
all riser lengths except 0 (no riser) where all the three con-
figurations have substantially the same system drag coefficient.
The 64 in. ribbon qnd the 48 in. ribless guide surface
configurations have appreciably the same system drag coefficients
for all riser lengths tested.
Figure 39 presents the average system drag coefficient
for all types of container-parachute configurations with risers
up to 30 ft full scale. The average component drag coefficients
and the sunmation of the component drag coefficients are also
given in every case.
Figure 40 fraphically illustrates the average system
drag coefficients of various container-parachute combinations
with the different riser lengths affording a ready means of
comparing the different configurations and the effect of riser
length for the same configuration.
a.6.3 Parachute and Container Free Attitude Angles
After recording the moment and drag characteristics of
the different configurations with risers, the locking arrange-
ment on the pivotal shaft was released, the container angular
measuring device and the parachute attitude measuring device
were activated and the free attitude angles a , 8 , and *
for different sizes of the ring slot, ribbon, and ribless
guide surface parachutes in conjunction with the A-22 Container
models with risers representing 10, 20, and 30 ft full scale
-63-
DRAG COEFFICIENT BASED ON
CONFIGURATION AN) RISER CONTAINER BASE AREAFULL SCALE LENGTHPARACHUTE (FT) CDp CDC CD+CDC CDS
DIAMETER (IN.) (FMACHUTE 4(PARACHUTE) (CONTAINER) CONTAINER) (SYSTEM)
0 2.19 0.95 3.14 2.66
RING SLOT 10 2.10 0.95 3.05 3.11
20 2.14 0.95 3.09 3.01
Do= 96 IN. 30 2.06 0.95 3.01 2.88
0 1.99 0.95 2.94 2.38
RIBBON 10 1.98 0.95 2.93 2.6520 1.96 0.95 2.91 2.59
Do= 96 IN. 30 1.94 0.95 2.89 2.81
0 1.90 0.95 2.85 2.55RIBLESS GUIDE 10 1.85 0.95 2.80 2.66
SURFACE 20 1.83 0.95 2.78 2.48
c= 72 IN. 30 1.73 0.95 2.68 2.31
0 0.97 0.80 1.77 1.17
10 o.94 o.80 I.74 1.89RING SLOT
20 0.88 o.8o 1.68 2.05
Do 64 IN. 30 0.85 0.80 1.65 1480
0 0.89 0.80 1.69 1.16
RIBBON 10 0.88 0.80 1.68 1.7720 0.85 0.80 1.65 1.80
Do = 64 IN. 30 0.88 0.80 1.68 1.87
0 0.85 0.80 1.65 1.23RIBLESS GUIDE
SURFACE 10 0.80 0.80 I.6o 1.6520 0.80 0.80 1.60 1.65
t4= 48 IN. 30 0.80 0.80 1.60 NO DATA
FIG. 39- AVERAGE DRAG COEFFICIENTS FOR A- 22 CONTAINER AND VARIOUS
PARACHUTE SIZES AND TYPES WITH 'VARIOUS RISER LENGTHS.
-64 -
+j 4-j
00 0 j
0N __ _ _ z
+. *J4)):
0
[T1SIio-is ONIb ~v
H
oD
W0 (_____Z __ 0)L117 43ISS N0B U! 6 WJ
V4JSRk R)i CN) U!9
U)
R~ KL0~ dO VGtNIA 0 U
were recorded. Figure 41-A, B, and C are photographs of the
experimental arrangement representing the A-22 Container in
combination with the 64 in. ring slot and ribbon parachutes
and the 48 in. ribless guide surface parachute with risers
representing 10 ft full scale.
Typical galvanometer traces representing the instan-
taneous free attitude angles a and 9 for the three types of
parachutes with risers representing 10 ft full scale are given
in Figs 42-A, B, and C.
Using the galvanometer traces for the deflection angles
a and e , mean values of these angles were calculated for each
configuration and riser length. As indicated in Paragraph 3.5.3,
the weight of the parachute model tends to produce an angle
which, because of the horizontal disposition of the riser and
parachute axis, is not representative of actual aerial delivery
conditions where the path is essentially vertical for most of
the trajectory after full deployment, Therefore the angle 4r
will not be considered.
The mean values of the angles 8 versus a for the
different riser lengths are illustrated in Figs 43-A, B, and C
for the ring slot, ribbon and ribless guide surface configura-
tions respectively.
We do not suggest that the free attitude angles, as
recorded by the galvanometer, represent quantitatively the
full scale free flight case. Furthermore, the equilibrium
angles appear to depend to a certain extent on the initial
rigging alignment. However, the tests give a useful indication
-66-
A. MODEL ARRANGEMENT
REPRESENTING CONTAINERAND 2o/ POROSITY 64" DIA.RING SLOT PARACHUTE
B. MODEL ARRANGEMENTREPRESENTING CONTAINERAND 20o/. POROSITY 64A
DIA. RIBBON PARACHUTE
, -. -- -- C. MODEL ARRANGEMENT
REPRESENTING CONTAINERAND 48' DIA. RIBLESS GUIDESURFACE PARACHUTE
r1
FIG. 41- EXPERIMENTAL ARRANGEMENT OF THE /4 SCALE A- 22CONTAINER IN COMBINATION WITH THREE PARACHUTE TYPES
WITH lOFT RISERS
-6'7-
I ~ I ofa ku-; I *2
~ in
k- I% J
I -C
ki~
Io in tn-
(s33930
I I-68-
I. _ I~ 771/ 1-10
.-.- I. "- . .. . ... . 4. _I F W 96 NO RISER I
*,9601 ClOIE 0 . 7 .y
.1 i - o' +) - idI,
- --- -2 0 " 2 4 4 -2 4 6 "
0 GA( "A - 2(- 10'
A.- /6 SCALEO 4 N MODEL S EPRESEN TINO NR W H 014 A. " - I/ A ND /4 SCALE. MODELS REPRENTING CDNTAINER WitTS D0. FLAT ,RAC A.A NUT 96 AND 4" OIA RING OT ACHUTE
F404-.M -- T.UE ,-GE. - -cru - -6----SO -E Oi IE N VROSF AfT'%V
MA , -NO RIS EN T R17'DA NO ROCA4 Id, " 10'
'A 0 1 i4.I * 4 A 4(1(1 1~S 4" 10 .4 11 46" 1 diA z-d ~" 2(f
oBE.
i -I, 2- I- -I I-
-4-2 0 2 A
C- 1/C AND 0/4 qCAi, MES REPRC ESWETEING CMIAAA WIt/I 967 AND 66" C - I& AND 1/4 SCALFE MODELS OEOAESCNALW A NYEA44C wit, 7e"IA RMSON PAACHUTE5 AND 4e6606RE U SOACE PARACHUTE
FIG, 41-. ME- AN A!IlrUDE~ ANGLES - VLH3IS 0 FOR MODIFLS ()F A-22 CONTAINER AND) VARIOUS PARAVI)JTFS WTHDIFFERENT RISER tLNGRTHS
-69-
of the general behavior and relative merits of the different
configurations.
IV. CONCLUSIONS AND GENERAL REMARKS
4.1 Conclusions
The experimental results presented in Section III, cover
a wide range of configurations involving three different scale
models of the A-22 Container, each stabilized by four different
types of parachutes using risers representing 0, 10, 20, and
30 ft in full scale.
In addition to the moment characteristics at different
angles of attack of tn container's longitudinal axis relative
to the air flow, the drag at zero angle of attack and the equili-
brium angle of attack of the container ( a ) and the attitude
angles ( 0 and * ) of the parachute axis with respect to the
container's longitudinal axis were recorded thereby providing
additional information on the relative merits of the different
parachute types as stabilizers and retarders for the A-22
Contpincr. From the resulto of these experiments, the follow-
ing general conclusions may be made:
a) The maximum height configuration of the A-22
Container (60 in. full scale) has the more critical stabiliza-
tion requirements, i.e., it has the smaller stable range and
stable moment coefficients in that range and the larger
destabilizing moments outside that range.
b) Without risers, the A-22 Container may be
stabilized by means of parachutes having a nominal diameter,
-Y0__
Do = 96 in. for the solid flat, ring slot (20% porosit.) or
ribbon types (20% porosity) and having a projected diameter
D = 72 in. for the ribless guide surface type.p
c) With a minimum riser length of 10 ft, the A-22
Container may be stabilized over the full angular range by
means of parachutes having a nominal diameter DO = 64 in. for
the solid flat, ring slot, or ribbon types and a projected
diameter Dp = 48 in. for the ribless guide surface type.
d) The use of risers greatly helps in stabilizing
the container, particularly for the relatively large scales
and more especially at large angle of attack. There appears,
however, to be an optimum length of riser beyond which the
moment coefficient does not increase with increase of riser
length and in some cases even tends to decrease.
e) The system drag coefficient is greatly increased
by using a riser and, in most cases, with a minimum riser of
10 ft full scale, it becomes substantially equal to the sum of
the drag coefficients of the container and parachute models
taken separately when both are referred to the container base
area.
f) From a visual observation of model behavior in
the wind tunnel and a study of the free attitude angles of the
container and parachute, we find that the configurations involving
the solid flat parachute, with or without risers, exhibit large
amplitude random motion and violent oscillations. It is con-
cluded that this type of parachute, despite its larger drag
and restoring moment coefficients, is the least suitable for
the proposed application.
-71-
The configurations involving the ring slot parachute
exhibited, in general, medium amplitude container deflections
and parachute oscillations and were decidedly more suitable
than those with the solid flat type.
The various configurations using the ribbon and ribless
guide surface parachute types produced, in general, much smaller
amplitude container deflections and parachute oscillations and
appeared to be quite satisfactory. The frequency of oscillation
of the parachute was higher for the ribless guid& surface, but
the amplitudes were generally much smaller, and this type
appeared to be the most suitable one from the container and
parachute deflection point of view.
4.2 Additional Remarks
The aerodynamic parameters presented in the preceding
chapters appear to be satisfactory for trajectory calculations
from which the performance characteristics and operational
requirements of the various combinations could be estimated.
This Document
Reproduced FromBest Available Copy
-72-
This DocumentReproduced From
REFERENCES Best Available Copy
1. Department of the Army Technical Manual, TM 10-530,
June, 1952.
2. United States Air Force Parachute Handbook, WADC TR
55-265, December, 1956.
3. White, Gerald B.: Principles of High Velocity Dropping
of Aerial Cargo, Parachute Engineering and Retardation
Summer Course, July 14-25, 1958, University of
Minnesota.
-73-
